NOIL1SM4000A Datasheet, PDF (14/30 Pages) ON Semiconductor – LUPA4000: 4 MegaPixel High Speed CMOS Sensor

NOIL1SM4000A
Timing specifications for each signal are shown in
Table 6.
• Falling edge of precharge is equal or later than falling
edge of Vmem.
• Sample is overlapping with precharge.
• Rising edge of Vmem is more than 200 ns after rising
edge of sample.
• Rising edge of reset is equal or later than rising edge of
Vmem.
Table 6. TIMING SPECIFICATIONS
Symbol
Name
Value
a
Mem_HL
5 − 8.2 ms
b
Precharge
3 − 6 ms
c
Sample
5 − 8 ms
d
Precharge−Sample > 2 ms
e
Integration time
> 1 ms
The timing of the pixel array is straightforward. Before the
frame is read, the information on the photodiode must be
stored onto the memory element inside the pixels. This is
done with the signals Mem_hl, precharge, and sample.
When precharge is activated, it serves as a load for the first
source follower in the pixel. Sample stores the photodiode
information onto the memory element. Mem_hl pumps up
this value to reduce the loss of signal in the pixel and this
signal must be the envelop of precharge and sample. After
Mem_hl is high again, the readout of the pixel array starts.
The frame blanking time or frame overhead time is thus the
time that Mem_hl is low, which is about 5 ms. After the
readout starts, the photodiodes can all be initialised by reset
for the next integration time. The minimal integration time
is the minimal time between the falling edge of reset and the
rising edge of sample. Keeping the slow fall times of the
corresponding internal generated signals in mind, the
minimal integration time is about 2 ms.
An additional reset pulse of minimum 2 ms can be given
during integration by asserting Reset_ds to implement the
double slope integration mode.
Readout of Image Sensor
When the pixel information is stored in the memory
element of each pixel, it can be read out sequentially.
Integration and readout can also be done in parallel.
The readout timing is straightforward and is controlled by
sync and clock pulses.
Figure 15 shows the top level concept of this timing. The
readout of a frame consists of the frame overhead time, the
selection of the lines sequentially, and the readout of the
pixels of the selected line.
Readout frame I
FOT
ROT
Readout Lines
Readout Pixels
Integration I+2
___
___
L2048
C2048
Figure 15. Readout of Image Sensor (L: line selection, C: column selection)
The readout of an image consists of the FOT and the
sequential selection of all pixels. The FOT is the overhead
time between two frames to transfer the information on the
photodiode to the memory elements. Figure 14 shows that
at this time Mem_hl is low (typically 5 ms). After the FOT,
the information is stored into the memory elements and a
sequential selection of rows and columns makes sure the
frame is read.
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